Global-scale Winds
Courtesy: U. of Alaska
General Circulation
> Global wind systems
General circulation
1-cell, 3-cell models,
comparison to real world
> Semi-permanent pressure
features
> Jet streams
02.23.2010
Scales of Motion - Hierarchy
planetary
scale
Longwaves
synoptic
scale
Hurricanes
Topical storms
Thunderstorms
Tornadoes
Waterspouts
Dust devils
mesoscale
microscale
Weather Map
Highs and Lows
Weather fronts
Land/sea breeze
Mtn/Valley breeze
Chinook
Santa Ana
Small turbulent
eddies
seconds
to
minutes
minutes
to
hours
hours
to
days
days
to
weeks
Atmospheric General Circulation
+ Large-scale, hemispheric flow
+ Average wind patterns across globe
+ Interrupted by highs and lows
moving through
UNEQUAL HEATING
OF THE EARTH
+ DRIVING FORCE??
COLD
WARM
THERMAL
IMBALANCE
COLD
Atmospheric General Circulation
UNEQUAL HEATING OF
THE EARTH
THERMAL IMBALANCE
COLD
Net LOSS
WARM
Net GAIN
Net LOSS
Energy Imbalance
COLD
Driver of Atmospheric Circulation
Models of Atmospheric Circulation
Single-cell Model
Assume
1) aqua planet
2) sun over equator
3) non-rotating earth
COLD
WARM
COLD
Models of Atmospheric Circulation
Single-cell Model
Assume
1) aqua planet
2) sun over equator
3) non-rotating earth
high
pressure
Result
>excessive heating at
equator
>thermally-driven
convection cell
low
>pole-ward flow aloft
equator-ward flow sfc
>termed, Hadley cell
The Atmosphere, 8th edition, Lutgens and Tarbuck, 8th edition, 2001
Models of Atmospheric Circulation
Three-cell Model
Assume
1) aqua planet
2) sun over equator
3) non-rotating earth
Result
>excessive heating at
equator
>thermally-driven
convection cells
>deflection of winds
>Hadley cell
Ferrel cell
Polar cell
The Atmosphere, 8th edition, Lutgens and Tarbuck, 8th edition, 2001
Atmospheric Circulation Models vs Reality
Idealized winds
Actual winds
The Atmosphere, 8th edition, Lutgens and Tarbuck, 8th edition, 2001
Atmospheric Circulation Models vs Reality
Actual winds
Why the difference?
1) land-water distribution
2) seasonality
unequal heating/cooling rates
Idealized winds
Atmospheric Circulation
Some Features of Note:
Equatorial
•ITCZ (Intertropical
Convergence Zone)
•Equatorial low
•Area of low wind speed
Doldrums (weak PG)
Atmospheric Circulation
Some Features of Note:
Subtropics
•Trade winds
•Horse latitudes
weak winds
•Subtropical high
warm and dry
Desert areas of the world
Atmospheric Circulation
Some Features of Note:
Midlatitudes, Polar
•Prevailing westerlies
•Polar front and areas of
low pressure
•Polar easterlies
Persistent Circulation Patterns NH winter
Sea level pressure and prevailing winds
Persistent Circulation Patterns NH winter
> subtropical highs
Sea level pressure and prevailing winds
Persistent Circulation Patterns NH winter
> 2 major subpolar lows: near polar front, storm track
Sea level pressure and prevailing winds
Persistent Circulation Patterns NH winter
> subpolar highs: shallow, thermally induced
Sea level pressure and prevailing winds
Persistent Circulation Patterns NH winter
> subpolar trough in SH: high winds and seas, roaring 40s
Sea level pressure and prevailing winds
Persistent Circulation Patterns NH winter
> ITCZ displaced south
Sea level pressure and prevailing winds
Persistent Circulation Patterns NH summer
> ITCZ displaced north
Sea level pressure and prevailing winds
Persistent Circulation Patterns NH summer
> Subtropical highs move north
Sea level pressure and prevailing winds
Persistent Circulation Patterns NH summer
> Thermal lows develop over land
Sea level pressure and prevailing winds
Persistent Circulation Patterns NH summer
> Weak Icelandic Low remains, Aleutian Low disappears
Sea level pressure and prevailing winds
Persistent Circulation Patterns NH summer
> Asian Monsoon season
Sea level pressure and prevailing winds
Seasonal Circulation Patterns
winter
summer
Strong thermal imbalance
Strong pressure gradient
Strong winds
Strong equator - pole temp gradient
Subpolar lows disappear
Subtropical highs remain
Zone of max heating shifts north
Weak equator - pole temp gradient
Thermal Imbalance is the Driver
Sea level pressure and prevailing winds
Seasonal Circulation Animation
L
H
Sea level pressure and winds
University of Oregon
Thermal Imbalance is the Driver
General Circulation and Precipitation
Dry
Wet
Wet Dry
Dry
Wet Dry
seasonally
Wet
Wet Dry
Dry
Wet
Dry
Wet Dry
General Circulation and Precipitation
Dry
Wet
Precipitation (mm)
University of Oregon
Jet Streams
• Fast-moving rivers of air
• High altitudes (~ 35000 ft) near
tropopause
• Long, shallow, narrow moving
west to east
• First observed during WW II
• Suspected earlier from ground
observations of fast-moving cirrus
Jet Streams
• Mark boundary between surface
air masses
• Shows ridges, troughs, eddies
• Changes in space and time
Jet Streams
• Seasonality
• Note the speed
differences
• Surface
temperature
differences
• Tend to steer
storm tracks
Jet Streams
Jet Streaks
Jet Stream and Jet Travel